(57) A flow of gas is conducted from a gas source to a high frequency oscillator. The high frequency oscillator comprises a housing (106) including a magnet (117) and having a diaphragmatically sealed piston (102) mounted therein, an inlet connecting the space within the housing (106) on the first side of the diaphragm (24) to gas conducting means (26), and a coil (120) mounted to the first side of the diaphragm (24). Circuitry is provided which is operable to reverse the polarity of the flow of the current in the coil (120), thereby causing the diaphragm (24) to move back and forth within the housing (106). A tube (25) connecting the space on the second side of the diaphragm (24) to the gas source and the patient's airway is provided. Also disclosed is a method of ventilating a patient with the high frequency oscillating ventilator, and a double lumen endotracheal tube for use in connection therewith.